The present invention is related to a method for testing multilayer tablets in a multiple rotary press, in which die holes of a circulating die plate are successively filled with tablet material of different layers in consecutive filling devices, and the tablet material is compressed layer after layer to pressed articles having n layers by means of synchronously circulating compression punches in compression stations respectively associated to the filling devices, and the pressed articles are subsequently ejected and unloaded in a unloading station, and wherein in a testing procedure, pressed articles having m layers are unloaded in an unloading station after the compression and are fed to a testing station, wherein 1<=m<n.
Rotary tablet presses for producing tablets from very different materials and for the most different application purposes are commonly known. A die plate driven around a mostly vertical axis has dies arranged in a circle for this purpose, to which are associated pairs of compression punches circulating synchronously with the plate. The actuation of the compression punches takes place by radial cams and compression rollers. During the filling of the die holes with the usually powder-shaped tablet material by means of a suitable filling device, the lower punch of a pair forms the bottom of a moulding cavity, wherein its height in the die pre-sets the dosage. Subsequently, the compression of the tablet material to a desired height (the cylindrical height) takes place by moving the opposing compression punches towards each other in a compression station. The compression station has normally a pre-compression station and a main compression station. Following the compaction, the lower punches, controlled by an ejection cam, thrust the tablets out of the die at a certain position of the machine, while the opposing row of punches (the upper punches) gradually moves out of the die plate. Through this, a stripping device can strip off the ejected pressed articles from the die plate and supply them to a discharge channel.
For the manufacture of tablets having two or more layers with a rotary press of the mentioned kind, the respective described stations are provided repeatedly, according to the number of the envisioned layers. In this, a first layer is filled in a first filling device at first, and slightly compacted by means of the compression punches. Through the rotation of the die plate, the die hole filled with the first layer arrives at a subsequent filling device, in which the second layer is filled in above the first layer. This second layer is then slightly compacted again. This procedure is repeated for so long until the last layer of the tablet which is to be produced (the n-th layer) has been filled into the die hole. After filling with the last layer, the compression to a multilayer tablet takes place, with subsequent unloading from the apparatus, as has been explained.
There is the necessity to test amongst others the weight of the produced tablets, and to perform a correction as the case may be. Therefore, one or several discharge channels may be provided in the press with discharge distribution switches, which selectively direct arriving tablets into the direction of a testing station. Testing stations, in which the testing procedures are automatically performed, like a weight measurement for instance, are also already known. In order to be able to determine even in a multilayer tablet which one of the layers is defective when there is a deviation from a desired weight, there is the necessity to check the weight of individual layers of the tablet. A corresponding testing method for a double layer tablet is known from DE 42 18 122 C1, for instance. In this, pressed articles with the first layer are unloaded after the compression in a testing procedure and conveyed to a testing station, where the weight of the first layer is measured. In order to facilitate the ejection of the pressed article consisting of only one layer in this, and in order to prevent that uncompressed material is accumulated on the die plate and in the remaining area of the press, before the unloading for a test, the first layer of the pressed article is compressed more strongly than this is the case during the normal manufacture of the multilayer tablets.
Here, a problem arises in that the force conditions and with this the vibration behaviour of the tablet press are changed by the stronger compression. This in turn leads to a changed filling of the die holes with the individual layers and through this to changed layer weights. The measured weight of layer samples taken under these conditions is therefore not always representative for the tablets formed with the plant in the normal operation. According to the application with the serial number 10 2007 061081.7, also filed by the present applicant, this problem is resolved by unloading pressed articles having m layers for testing, by way of an unloading station arranged after the mth compression station and before the subsequent (m+1)th filling station. In this, only such pressed articles are supplied to the testing station, which had been completely filled with the tablet material of the mth layer already before the initiation of the testing procedure, i.e. which had already left the mth filling device. In this way, only layer samples are tested that are filled in a representative fashion. However, in this procedure the number of layer samples which is provided for testing is admittedly relatively small, because only pressed articles between the mth filling device and the unloading station arranged after the mth compression station and before the (m+1)th filling device can be used.
Starting from the state of the art that was set forth here, the present invention is based on the objective to produce representative layer samples that are not influenced by the process of taking samples in a method of the kind mentioned in the beginning, wherein the number of the usable layer samples is increased.